It would seem odd to help someone by "cracking" their back. Patients often use the term "crack" or "snap" for the sound associated with certain types of chiropractic procedures. The "pop" that is produced with this type of hands on technique is a result of a small amount of gas that gets released when pressure is applied to a joint, much like "popping" your knuckles. Other techniques do not produce this sound at all.
Patients then often ask why they can "crack" their own back. This is often a sign that some joints are working or moving too much, while others are not moving properly. The stress of the imbalance builds, this usually leads to greater problems though. If you or someone you know "cracks" their own back or neck repetitively, a chiropractic evaluation can help uncover reasons and actions to help prevent further problems from developing.